Recently, with the progress of a semiconductor integrated circuit manufacturing technique, a multi-element and high element-density semiconductor device have been developed. The progress of micro processing techniques in a semiconductor device manufacturing makes it possible to manufacture a very large scale integrated circuit (VLSI) employing a 1.5 m or 1 m rule. However, the manufacturing of such VLSI gives rise to various problems due to a miniaturization of the device. One of these problems is a "narrow channel effect" by which a threshold voltage V.sub.T is increased as a channel width of a transistor is narrowed. This effect causes disadvantages because a driving voltage, which is higher than a necessary voltage, must be applied to the device; or, not enough electric current can flow in the device to drive it. This means that necessary signal charges cannot be handled in a charge coupled device (CCD).